1. Field of the Invention
The present invention relates to an abnormality detection apparatus for a secondary battery device, which detects an abnormality of over-charging or over-discharging in a secondary battery, and which is advantageously mounted on a battery pack, together with, e.g., lithium ion secondary batteries.
2. Description of Related Art
Generally, as a power source for electric power tool, system backup, or the like, one having 5 or more, e.g., 7 lithium ion secondary batteries connected in series for obtaining a large electric current is used.
Lithium ion secondary batteries are easily affected by over-charging or over-discharging, and, when the battery is used at a voltage beyond a predetermined range, there is a possibility that the materials used in the battery decompose and the capacity is markedly lowered or the battery suffers uncontrolled temperature elevation, thus making it difficult to use the battery normally.
For this reason, in the use of a lithium ion secondary battery, generally, the upper limit voltage and lower limit voltage of the battery are definitely specified, and charging or discharging of the battery is controlled so that the terminal voltage falls in this range, or the battery and a protecting circuit for restricting the voltage to the range are used in combination.
An abnormality detection apparatus for a secondary battery device is disclosed, for example, in Japanese Unexamined Patent Application Publication No. 2001-174531 (Patent Document 1). The abnormality detection apparatus disclosed in the Patent Document 1 detects an abnormality in charging or discharging with respect to an assembled battery which includes a plurality of cell groups connected in series in which each cell group having connected in series a plurality of unit cells including a secondary battery.